I really like the results from the home-made flash (large white paper envelope) refelctor I used on my SB-900 last Saturday at the Laguna Seca track. This Sunday is the Concours at Pebble Beach.
My options from most to least expensive include the large Expolmaging Rogue Flashbender from the local camera store, or a cut to fit piece of white plastic polystyrene (a plastic supply company is down the road from me), glossy white cardboard, or another white envelope. This is what's available to me right now and will all provide a 9-inch by 9-inch surface of varying reflectivity. The Flashbender provides a greater degree of flexibility.
If there's something else available that's better than the Flashbender, I can go to the less expensive options and order.